PROJECT SUMMARY/ABSTRACT PROJECT 9: DIFFERENTIAL DIAGNOSIS OF OTITIS MEDIA Otitis media (OM) is the most common cause of conductive hearing loss (CHL) in children and the leading cause of pediatric office visits, prescription antibiotic use, and pediatric surgery. While a number of clinical research studies demonstrate that OM can lead to long-lasting perceptual auditory deficits, numerous other studies suggest that the long-term impact of OM is minimal. In contrast, basic studies of OM in animal models show far less ambiguity in their outcomes, strongly suggesting a direct link between OM and longstanding auditory processing deficits. A potential cause of the equivocal findings in the clinical research literature is the heterogeneity of OM. OM is an umbrella term generally used to broadly define all types of middle-ear dysfunc- tion due to infection and/or middle-ear effusion. OM may or may not include an inflammatory infectious disease process, and effusions present in OM may be serous, mucoid, or purulent, and vary considerably in both vis- cosity and volume. OM is often accompanied by CHL, but the degree of this CHL can vary from 0-40 dB. The OM-related factors determining degree of CHL are not known. Clinical studies often focus simply on the pres- ence of OM, and systematic documentation of these OM-related variables is limited, at least in part because there is no objective method to differentiate variations in OM in clinical populations. The long-term goal of this work is to understand how differences in OM affect long-term outcomes. Improvements in the differential diag- nosis of OM are necessary to adequately quantify severity and classify the variation in this group. As a first step, the purpose of this specific proposal is to improve the differential diagnosis of OM. These experiments will systematically investigate the mechanical effects of various types of OM and the effusions that accompany them, and determine how variations in OM influence degree of CHL and afferent auditory transmission at the level of the brainstem. This will allow us to subdivide this heterogeneous population by identifying OM-related variables, and tools to measure them, that may be useful in identifying children with OM who are at higher-risk for long-term deficits. Aim 1 will determine if a non-invasive objective measure of tympanic membrane mobility, wideband acoustic immittance (WAI), can be used to differentially diagnose two common types of OM, Acute Otitis Media (AOM) from Otitis Media with Effusion (OME) as well as detect differences in effusion characteris- tics including effusion volume, viscosity, and purulence. Aim 2 will investigate how differences in OM effusion characteristics influence the quality of the afferent auditory signal and degree of conductive hearing loss. The results of the proposed study will lead to more effective and evidence-based treatment protocols and reduce the likelihood of antibiotic prescription where it is not indicated. In addition, these studies will provide crucial diagnostic information not currently available as to how a specific episode of OM degrades the quality of audi- tory input and will guide providers on whether aggressive management of a case of OM may be warranted.